Spiritual v. Political Constructs

How do I explain a spiritual construct to a nine-year-old?  My granddaughter told me that she didn't want to be Catholic any more because girls can't become pope.

I blame her teacher from last year.  She had to do a report on Vatican City and she was told that women couldn't  vote, which isn't true.  Nobody votes in Vatican City. I told her that but evidently it didn't stick. 

But about girls not able to be pope.  She's applying a political construct to a spiritual one.  How do you explain that to a child?

The pope is a pastoral position.  The pope is the head of the church family.  The pope is the Vicar of Christ.  The pope is the successor of Peter.  All these positions are male.

I think I'll wait until she is a teenager to tackle why girls can't become pope.